Enhanced support for limits and timeouts.

* Add support for request size limits
* Add support for bandwidth limits
* Expose keep-alive parameters
* Move to 1.3
What about changing this call to look like this:

```
if l.isRequestOverLimit(req) {
    return re, errors.FromStatus(http.StatusRequestEntityTooLarge)
}

...

func (l*HttpLocation) isRequestOverLimit(req request.Request) {
    if l.options.Limits.MaxBodyBytes <= 0 {
        return false
    }
    if (req.GetHttpRequest().ContentLength < l.options.Limit.MaxBodyBytes) {
        return false
    }
    return true
}
```